Switched local area networks use a network switch for supplying data frames between network stations, where each network station is connected to the network switch by a media. The switched local area network architecture uses a media access control (MAC) enabling a network interface within each network node (including the switch) to access the media.
The network switch passes data frames received from a transmitting station to a destination station based on the header information in the received data frame, including source address and destination address. One arrangement for generating a frame forwarding decision uses the source address and/or destination address in a direct addressing scheme, where the network switch includes a table storing switching logic for a plurality of network addresses, and where the switching logic for the corresponding destination address is stored in a table address corresponding to the destination address. Such an arrangement, however, is not practical for a network where the source addresses or destination addresses may have a large variation in values. Moreover, it may be more difficult for the network switch to quickly scan a table for the referenced address, locate the address, and make a frame forwarding decision as the table grows with table entries storing address information, especially if the address information is stored in a sequential manner. Since multiple data frames may be received by the network switch simultaneously, the network switch needs to make frame forwarding decisions relatively quickly. Hence, storing address information in a sequential manner (i.e., arranged in an increasing order by either source address or destination address) becomes impracticable as the number of entries increases, since a row by row search for the appropriate address table entry may be too slow for making frame forwarding decisions for multiple received data frames.
One arrangement for improving the accessing of switching logic from a table involves hashing, where an address, such as the source address or destination address, is transformed into a key that will be used to access information from a table. A problem with using a hash function is that the hash function is permanently set in the network switch. Hence, network traffic over time may cause over-usage of certain entries in the address table of the network switch. Hence, the over-usage results in a loss of efficiency in accessing the appropriate address table entry, causing the switching engine in the network switch to suffer a loss of performance in the throughput in making frame forwarding decisions.
In addition, the network switch may simultaneously receive data packets from multiple switch ports, requiring that the switching engine in the network be capable of making frame forwarding decisions as fast as possible to minimize loss of performance and backlog. However if the switching engine is required to generate hash keys for multiple switch ports simultaneously (for both source and destination addresses), then the substantial processing requirements may greatly increase the cost of the network switch.